Touchpads have been widely used in electronic products including portable computers, personal digital assistants (PDAs), mobile phones, and other electronic systems. By sliding or touching on the operation area of a touchpad with a finger or other object, the relative movement or absolute coordinate movement of a cursor, or other extended functions such as simulated buttons, may be implemented. A conventional touchpad is constructed by a four-layered printed circuit board (PCB) structure, as shown by a cross-sectional view of FIG. 1, which comprises X-directional traces 104 provided in a first layer of a PCB 102, Y-directional traces 108 provided in a second layer of the PCB 102, an insulator layer 106 between the X-directional traces 104 and the Y-directional traces 108, a ground layer 112 provided in a third layer of the PCB 102, an insulator layer 110 between the Y-directional traces 108 and the ground layer 112, a component layer 118 in a fourth layer of the PCB 102, an insulator layer 114 between the ground layer 112 and the component layer 118, and an insulator cover 122 over the PCB 102 for providing an operation area thereon. The X-directional traces 104 and the Y-directional traces 108 are connected to the component layer 118 via through-holes 116 and 120, respectively. Although the ground layer 112 is proven not necessary by experiments, thereby simplifying the four-layered PCB structure to three-layered structure, the cost of such touchpad is still not reduced effectively.
For cost down, it was developed a touchpad with two-layered PCB structure, whose cross-sectional view is shown in FIG. 2. Such touchpad comprises X-directional traces 204 as shown in FIG. 3A, located in the top layer of a PCB 202, Y-directional traces 208 as shown in FIG. 3B, together with a component area 210 on the periphery therearound located in the bottom layer of the PCB 202, an insulator layer 206 between the X-directional traces 204 and the Y-directional traces 208 together with the component area 210, and an insulator cover 214 over the PCB 202 for providing an operation area thereon. The X-directional traces 204 are connected to the component area 210 via through-holes 212, while the Y-directional traces 204 are connected to the component area 210 directly without through-holes. A top view of the PCB 202 shown in FIG. 2 is provided in FIG. 4 in which the X-directional traces 204 and the Y-directional traces 208 are located in corresponding areas in the top layer and bottom layer, respectively, of the PCB 202, and the component area 210 is located in the peripheral area around the Y-directional traces 208 in the bottom layer. FIG. 5 shows a structural diagram of the bottom layer of the PCB 202 illustrated in FIG. 2 in which, the X-directional traces are connected to a controller 216 in the component area 210 via the through-holes 212 and further to other components 218, while the Y-directional traces 208 are directly connected to the controller 216 in the component area 210 and further to the other components 218.
To maintain the two-layered PCB structure and four-layered PCB structure have substantially the same area such that they could be replaced with each other without any change of mechanism design for convenient modulization, it is further developed a two-layered structure having a cross-sectional view as ahown in FIG. 6, which comprises X-directional traces 604 and Y-directional traces 606 both provided in the top layer of a PCB 602, a component area 616 provided in the bottom layer of the PCB 602, an insulator layer 608 between the X-directional traces 604 and the Y-directional traces 606 together with the component layer 616, and an insulator cover 614 over the PCB 602 for providing an operation area thereon. Due to the X-directional traces 604 and the Y-directional traces 606 both in the top layer of the PCB 602, they need through-holes 618 and 620 to connect to the component area 616 in the bottom layer, respectively. Moreover, for the purpose of avoiding short circuit resulted from the intersections of the X-directional traces 604 and the Y-directional traces 606, the Y-directional traces 606 are not directly interconnected therebetween, but interconnected with carbon film wires 612 formed by carbon ink printing. An insulator 610 is additionaly provided between the X-directional traces 604 and the carbon film wires 612 to avoid short circuit therebetween. FIG. 7 is a structural diagram of the top layer of the PCB 602 having the carbon film wires 612 to interconnect the Y-directional traces 606. Although the touchpad with two-layered PCB structure has lower cost than that of the touchpad with four-layered PCB structure, it is still not enough to satisfy the requirement of users on the price. Additionally, the carbon film wires printed on the two-layered PCB structure will be worn out as it is used, resulting in shorter lifetime of the touchpad.
Therefore, it is desired a touchpad with single-layered PCB structure to havelower cost and longer lifetime.